Pick a number

Numbers in JavaScript are represented as floating point numbers. The integer 42 and the number 42.0 have the same representation. This is convenient for working with numbers because you do not need to worry about whether a number is an integer or floating point.

Underneath it all, JavaScript uses 64 bits to represent each number. Why do you need to know that each number in JavaScript is 64-bit? Usually you do not need to care that a number is 64-bit. However, if you are working on a program that uses very large numbers, you would have to worry about whether 64 bits are enough for your purpose. Use the program number.js below to help you determine the smallest and largest numbers that can be represented on your computer. My computer has a 64-bit CPU and the results of the program running on my computer are given in the comments. As you can see, the largest safe integer I can have on my computer is a little over 9 quadrillion and the smallest safe integer is the negative of the largest safe integer.

number.js

1
2
3
4
5
6
7
8
9
10
11

/**
 * Largest and smallest numbers in JavaScript.
 *
 * @param {NS} ns The Netscript API.
 */
export async function main(ns) {
    ns.tprint(Number.MIN_VALUE); // 5e-324
    ns.tprint(Number.MIN_SAFE_INTEGER); // -9007199254740991
    ns.tprint(Number.MAX_VALUE); // 1.7976931348623157e+308
    ns.tprint(Number.MAX_SAFE_INTEGER); // 9007199254740991
}

Look again closely at the comments in the program. Why is the letter e in two of the numbers? A number written as 5e3 or 1.5e4 is using scientific notation. The letter e here means “exponent”, telling you the exponent to which you must raise 10. Consider the number 5e3. You write down 5. The part e3 tells you to raise 10 to the power of 3, i.e. 1000. Now multiply 5 by 1000 to obtain 5,000. Thus 5e3 is a compact representation of the expanded form 5,000. By way of another example, the number 1.5e4 means that you write down 1.5. Raise 10 to the power of 4 to get 10,000. Now multiply 1.5 by 10,000 and you have 15,000, which is the expanded version of 1.5e4. As you can see, the e (or scientific) notation is handy whenever you want a compact representation for a large or small number. Do you want to write 7 million in your program as 7000000 or as 7e6?

Special numbers

JavaScript defines three special numbers: NaN, positive Infinity, and -Infinity. The symbol NaN means Not-A-Number. It results when a number conversion fails or an operation cannot be performed on two numbers, among other reasons. For example, you would get NaN if you try to evaluate 0 / 0. In some programming languages, attempting to divide zero by zero would result in the immediate halt of your program. JavaScript is lenient, but you still need to guard against having something as absurd as 0 / 0 in your programs. The symbol NaN can also be accessed as Number.NaN.

Positive Infinity is defined in JavaScript as the number greater than every other number in the language. Similarly, the special number -Infinity is defined as the number smaller than every other number. These two numbers are useful in certain situations, but do not expect them to behave like their formal mathematical definitions. The special numbers Infinity and -Infinity are the same as Number.POSITIVE_INFINITY and Number.NEGATIVE_INFINITY, respectively.

Variables

A variable in programming languages is like a named box that can hold a value. You place a specific value into the box. Anytime you want to use the value, you reference the name of the box. One way to create a variable in JavaScript is by using the keyword let. Suppose you want to assign the number 7 to a variable whose name is number. In JavaScript, you would do it like so:

variable.js

1
2
3
4
5
6
7
8
9

/**
 * Create a variable and print its value.
 *
 * @param {NS} ns The Netscript API.
 */
export async function main(ns) {
    let number = 7;
    ns.tprint(number);
}

Note the equal sign =. In JavaScript, and indeed in many other programming languages, the equal sign = does not mean mathematical equality like you have been taught in mathematics classes during your school days. Instead, the equal sign = is used in JavaScript to mean “assign”. The statement let number = 7; in effect says, “Let’s create a variable called number and assign the number 7 to the variable.” From hereon, whenever you want the numeric value 7, you can use the variable number instead.

The keyword let is flexible. Once you have declared a variable using let, you can assign a value to that variable. Later on in your program, you can assign a different value to that same variable. There are cases where you do not want a variable to have a value other than the value you first assigned it. An example is the number of days in a week, namely 7. The number of days in a week remain the same no matter which country you are in, unless you happen to be in a country that uses a different kind of calendar. In JavaScript, how do you declare as constant a variable that holds the number of days in a week? Do so using the keyword const, as shown in the script below.

week.js

1
2
3
4
5
6
7
8
9
10
11
12
13
14

/**
 * A variable whose value can be changed and
 * another variable whose value cannot be changed.
 *
 * @param {NS} ns The Netscript API.
 */
export async function main(ns) {
    let weekend = 2;
    weekend = 3;
    const daysInWeek = 7;
    ns.tprint(weekend);
    ns.tprint(daysInWeek);
    // daysInWeek = 5;
}

Exercises

Exercise 1. Write the number 420,000,000 in terms of scientific notation.

Exercise 2. Write the expanded form of the number 9.6e1.

Exercise 3. Why is the number 5e-3 different from -5e3?

Exercise 4. MDN Web Docs has up-to-date documentation about JavaScript. You should be consulting the JavaScript reference on MDN as you learn JavaScript. Spend some time to browse through the reference now. Do not worry if everything is incomprehensible at the moment. For now, it is more important that you are familiar with the structure of the reference rather than its contents.

Exercise 5. Read more about numbers in JavaScript here.

Exercise 6. JavaScript also allows you to handle huge integers that do not fit within 64 bits. Browse through the documentation of BigInt to see what JavaScript has to offer in terms of very large integers.

Exercise 7. Create a script called age.js. Assign your age to a variable and print the value of the variable to the terminal.

Exercise 8. Refer to the script week.js above. Uncomment the line

1

// daysInWeek = 5;

Save the script and run it again. What do you get as output? Why do you get such output?

Exercise 9. Apart from using let and const, a third way to declare a variable is by using the keyword var. You will most likely see var being used in JavaScript code sooner or later. Avoid using var in any JavaScript code you write. Stick to let and const as much as possible. Read this article to learn more about the differences between let, const, and var.

Exercise 10. The operator typeof allows you to query the data type of a variable or whatever value you give to the operator. Run the script below and note the output printed to the terminal. Why does the variable n have the data type number? Edit the script to print the data type of each of NaN and -Infinity.

typeof.js

1
2
3
4
5
6
7
8
9
10

/**
 * The data type of a variable.
 *
 * @param {NS} ns The Netscript API.
 */
export async function main(ns) {
    const n = 42;
    ns.tprint(typeof n);
    ns.tprint(typeof Infinity);
}